Int. Brokers spread tracking (RATIO)

I am an IB user, trying to track the RATIO between 2 stocks. I am using a Mac, which is not supported by their API software. No one at IB has been able to show me how to track the RATIO between 2 stocks using their basic TWS, although, using the combo function, you can track the PRICE DIFFERENCE between them. Suggestions on tracking a RATIO, anyone???